Satellite signal transmission techniques improve substantially to meet people's needs in many ways, such as communication, astronomical observation, meteorological observation, and so forth. As a result, the number of the operating satellites in space grows rapidly as the need for satellites increases in recent years. Sometimes, the space is so crowded that two satellites may even be set in almost the same orbit.
As to current techniques of satellite signal transmission, the Fixed-Satellite Service (FSS) is used to receive linear polarization signals with frequencies about 10.95 GHz to 11.7 GHz. The Broadcasting-Satellite Service (BSS) is used to receive circular polarization signals with frequencies about 12.2 GHz to 12.7 GHz. Those two types of satellite services have close frequency bands and usually are set in almost the same orbit. Thus, the corresponding receivers or feeds for receiving satellite signals must have the ability to receive linear polarization signals from FSS satellites and to receive circular polarization signals from BSS satellites. However, it is quite difficult to receive two types of signals by one single receiver or feed with current techniques. Also, the issue for avoiding interference between two types of signals needs to be solved for the time being. Therefore, receivers or feeds of the prior art are not able to take up the challenge. Instead, most traditional receivers or feeds could only receive one type of signals. For example, it takes two different feeds to receive linear polarization signals and circular polarization signals respectively.
As shown in FIG. 1, in the prior art, two antenna disks 11 and 12 are used to receive a linear polarization signal 111 and a circular polarization signal 121 respectively. This kind of method of implementing two antenna disks is quite uneconomical.
The U.S. Pat. No. 3,731,236 discloses an apparatus for transferring and receiving two types of signals. As shown in FIG. 2, the apparatus includes a transformer 14 connecting to a four-port ortho-mode transducer (OMT) 13. The four-port ortho-mode transducer (OMT) 13 connects to four rectangular waveguides 21, 22, 23, and 24 respectively. While receiving signals, low frequency signals are transferred through the four rectangular waveguides 21, 22, 23, and 24. However, when the transferred low frequency signals, including circular polarization signals, passing through the four rectangular waveguides 21, 22, 23, and 24, the circular polarization signals will be distorted or destroyed. That is to say, instead of receiving signals of any frequencies, the apparatus could only operates normally when the frequency of the linear polarization signals is lower than that of the circular polarization signals.
Consequently, with current techniques for satellite signal transmission, a novel apparatus and method for receiving all types of signals with any frequencies, without serious interference, is desired.